1. Field of the Invention
The concentration of thyroxine in the bloodstream is within relatively narrow limits critical to the proper functioning of the body. The concentration of thyroxine is extremely small and can only be detected in very sensitive techniques.
One technique which is employed for the determination of thyroid hormones is radioimmunoassay. While this technique has many variations, it employs the combination of an antibody for the thyroid hormone and radioactive or hot thyroid hormone with blood serum and a separation of the bound hormone from unbound hormone. The amount of hot hormone, which is bound to antibody or remains free, will be a function of the amount of hormone in the serum. By determining the radioactivity of the solution freed from antibody, one can calculate the amount of hormone based on standards employing known amounts of hormone.
The use of radioimmunoassay requires a separation step which introduces errors and can be time-consuming. In addition, one must work with radioactive materials which decay and, therefore, have a limited shelflife. Also, working with radioactive materials is generally undesirable because of health hazards. There is a continuing need for a simple technique which minimizes the manipulative steps, while providing a high degree of sensitivity.
2. Brief Description of the Prior Art
U.S. Pat. No. 3,817,837 describes an enzyme assay which is found to be generically useful for a wide variety of ligands.